Permanent dental implants have become a common method of replacing missing teeth. Prosthetic replacement teeth are supported by screws set into the jaw bone directly beneath the location where the tooth or teeth are missing and the replacement teeth are formed or mounted on the ends of the implant screw that protrudes above the gum line. The procedure of placing these screws into the jaw bone is done virtually blind by the dentist. As a result, there are many cases where implant screws are not properly placed, resulting in the failure of the dental implants and the removal and replacement of the implants with new implants or removable dental bridges anchored to adjacent teeth.
One important factor to the long term success of permanent dental implants resides in that the supporting screw is centered in the bone mass of the jaw at an angle directly under the load force that will be placed on the implant. The mechanical screw thread must be fully engaged with the jaw bone at a torque force that is less than the thread breakout force in the bone. The mechanical structure of implant screws is preferably such that it does not permit the implanted tooth to move or create pressure on the natural teeth next to the implants.
To ensure the pilot hole for the implant screw is properly placed, x-rays are taken, studied and reviewed to determine the best screw location and alignment. In most cases, the dental surgeon references the teeth he can see with x-rays or radiographs and positions the entry and alignment of the drill on visual observations. Conventional methods for dental implant placement typically involve freehand positioning based on subjective data such as visual examination with invasive bone structure exposure. Unfortunately, this method relies on specialist's skills and experience, extends the healing time and increases the risk of possible infection.
Custom fixtures that anchor on adjacent teeth with guide holes to properly align the drill have been attempted with limited success. Issues exist with the cost of fixture creation and the time required to place the fixture, and which unduly lengthen the time to the procedure, both in productivity for the doctor and comfort for the patient. As a result many dentists have reverted back to the freehand method, using the adjacent teeth as references to position and aligning the drill based on what was observed in the x-ray and accepting the failed procedures as the risk involved.
More sophisticated methods involve using cone-beam computed tomography (CBCT) data for implant placement planning, and CAD/CAM-based dental drill guide fabrication. The main utility of the guide is to transfer pretreatment planning information to the surgery site. The guide is usually made out of plastic and it is supported on residual or adjacent teeth, or in other cases attached with specially designed mini implants. Typically, such guides require the formation of metal sleeves which are immersed in plastic, and which act as jigs for positioning and depth control of the dental drill bit. Such system are personalized, entirely designed and fabricated based on pretreatment CBCT scans of the patient. Due to its complexity, involved risk and required accuracy, the guide fabrication is centralized and completed by professionals which increases the cost and considerably extending the restoration timeline.